1. Field of the Invention
This invention relates to insulation blankets for providing thermal and acoustic insulation for aircraft. More particularly, this invention relates to insulation blankets that contain fire-blocking materials for preventing rapid penetration of fire into an aircraft fuselage in case of a fire outside the aircraft.
2. Description of the Related Art
The passenger cabins of commercial passenger airplanes are insulated from temperature extremes and noise by the use of thermal/acoustic insulation blankets. Examples of such insulation blankets are described in U.S. Pat. No. 5,108,821 (Dooley, et. al.) and in U.S. Pat. No. 5,624,726 (Sanocki et. al.). Such insulation blankets are typically placed adjacent to the interior skin of the aircraft fuselage, between fuselage frame members that are typically parallel and spaced at regular intervals along the length of the fuselage. The insulation blankets are typically constructed to a uniform width to fit snugly between the fuselage frame members, and are attached to the frame members by means of connectors inserted through the selvedge of the insulation blanket. Other portions of the interior of the fuselage, such as the interior edges of the frame members, bulkheads, and ducts, are also insulated by means of blankets that are constructed to fit the particular portion to be insulated. The blankets have other features and qualities as described in U.S. Pat. Nos. 5,624,726 and 5,108,821, which are incorporated herein by reference.
Thermal/acoustic insulation blankets for aircraft are typically comprised of a fibrous lofted insulation such as fiberglass batting encased within a protective covering. The protective covering is typically made from primarily two pieces of lightweight, tear-resistant reinforced polymer films. The primary purpose of the protective covering is to prevent moisture from being absorbed by the fiberglass batting during the service life of the insulation blanket, to facilitate installation, and to protect the insulation batting from damage during installation. Other means for making the insulation blanket more rugged and impervious to moisture are available, but presently protective coverings made from lightweight reinforced polymer films are preferred. Typically a blanket is constructed by cutting two separate pieces of protective covering film to a shape slightly larger than the piece of batting to be contained. The two pieces of film are then joined together along the edges of the insulation batting to form a selvedge. The selvedge is typically a thin, ribbon-like structure between one-half inch and three inches wide, attached at its interior edge along a line roughly midway between the two major surfaces of the insulation batting and around the circumference of the insulation blanket. One function of the selvedge is to join and seal the two pieces of covering film together. The selvedge is also useful for attaching the insulation blanket to the aircraft frame as described below.
Insulation blankets are typically attached to the aircraft frame members using attachment posts, known in the industry as xe2x80x9cChristmas trees,xe2x80x9d fixed to the frame members at intervals along the length of the frame members. The selvedge of the insulation blanket is put over the attachment post. The selvedge is held in place on the attachment post by a washer. The washer is held in place by annular serrations on the attachment post which are oriented to permit the washer to be slid onto the post more easily than it may be removed. Another typical attachment method uses u-shaped spring clips to clip the selvedge of the insulation blanket to the aircraft frame.
Fire-blocking materials for incorporation into insulation blankets are known in the art. For example, heat-treated partially carbonized polyacrylonitrile fibers known by the trade name CURLON(copyright) may be formed into fire-blocking high-loft batts with a density of 0.2 to 1.0 pounds per cubic foot (pcf), typically 0.2 to 0.5 pcf. CURLON fibers are available from ORCON Corporation of Union City, Calif. , and are described in U.S. Pat. No. 4,837,076 (McCulloch et. al.). U.S. Pat. No. 4,897,303 (McCulloch et. al.) describes an insulation material made from CURLON fibers and suitable for use in aircraft. CURLON fibers may also be formed into felts and papers having densities of greater than about 1.0 pcf, typically 3 to 5 pcf. Other fire-blocking materials include ceramic materials such as refractory aluminoborosilicate and aluminosilica fibers known by the trade name 3M(trademark) NEXTEL(trademark), available from 3M Ceramic Fiber Products of St. Paul, Minn. U.S. Pat. No. 5,624,726 describes an insulation blanket incorporating a layer of NEXTEL fibers as a component. Other refractory materials, such as other ceramic fibers, basalt fibers, leached glass fibers, and rock wool, may also be used as fire-blocking materials if processed into a suitable form for use in aircraft insulation blankets.
The purpose for incorporating fire-blocking materials such as CURLON into insulation blankets is to protect the occupants of the aircraft in case of a ground fuel fire. A ground fuel fire, often called a xe2x80x9cpost-crashxe2x80x9d fuel fire, occurs when fuel spilled on the ground outside the fuselage of a grounded aircraft ignites. Survivable post-crash fuel fires have occurred in the past after crash landings that were not severe enough to cause the fuselage to be destroyed upon impact, but were severe enough to cause fuel to spill from the aircraft and ignite. Survival rates from such crashes may be improved if the occupants are protected from the fire long enough to evacuate the aircraft. If the fuel fire penetrates the fuselage interior too quickly, the occupants will be overcome by smoke and heat before they can evacuate the aircraft, and will perish in the fire.
Tests conducted by the Federal Aviation Administration have shown that a typical aircraft fuselage insulated with fiberglass will provide about 1.5 to 2 minutes of protection from an intense fuel fire, before flame penetration occurs. Insulation blankets made with fire-blocking materials such as CURLON and NEXTEL can provide over five minutes of protection. However, in order to provide this extended period of protection, the insulation blankets must remain in position after the aluminum skin of the aircraft is consumed or melted away (typically in 20 to 60 seconds). In addition, the fire-blocking insulation must be firmly secured to the aircraft frame members so that no gap forms between the edge of the blanket and the aircraft frame. Such a gap would provide a pathway for the penetration of flames into the aircraft""s interior, even if the insulation blanket remains generally in place.
Current methods commonly in use for securing insulation blankets to aircraft frame members will reduce the effectiveness of fire-blocking insulation blankets. The selvedge currently used to secure the insulation blanket will rapidly melt or bum when exposed to the heat of a fuel fire. When its selvedge is destroyed, the insulation blanket can fall away from the attachment post or spring clip holding it in place on the frame, allowing flames to penetrate into the interior of the aircraft. It is desirable for a fire-blocking insulation blanket to remain secured in place for at least two minutes, and preferably for more than five minutes, when subjected to a fuel fire. It is further desirable to secure fire-blocking insulation blankets to the aircraft frame members so that no gap permitting flame penetration forms between the aircraft frame members and insulation blanket when subjected to a fuel fire. Current insulation blankets and methods of attachment will not provide the desired duration and quality of attachment when exposed to a fuel fire.
The invention provides an insulation blanket for aircraft that includes thermal/acoustic insulation, such as lofted fibrous insulation, foam insulation, or a combination thereof, and one or more fire-blocking layers of material adjacent to the insulation and extending past the edges of the insulation so that at least one fire-blocking layer may be attached to the aircraft frame members along the edges of the insulation blanket. The insulation and fire-blocking layer or layers are preferably encased in a protective covering. The insulation and fire-blocking layer or layers may be, but need not be, adhered to one another.
In an alternative embodiment of the invention, the lofted insulation is made from a fire-blocking material so that a separate fire-blocking layer is not needed. The insulation is preferably encased in a protective covering. The insulation and insulation blanket are wider than the spacing of the aircraft frame members so that the edges of the insulation blanket may be attached to the aircraft frame members along the edges of the insulation blanket.
In an alternative embodiment of the invention, the fire-blocking layer is adjacent to or adhered to the outside surface of the protective covering on one side or both sides of the insulation blanket. The fire-blocking layer extends past the edges of the insulation so that the fire-blocking layer may be attached to the aircraft frame members along the edges of the insulation blanket. Preferably, the fire-blocking layer is treated with a water repellent substance or encased within a separate protective covering to prevent absorption of moisture. Depending on the method used to assemble the insulation blanket, this configuration permits easier joining of the edges of the protective covering encasing the lofted or and/or foam insulation. Furthermore, the fire-blocking material need not be attached to the protective covering, allowing it to exist as a separate piece until the insulation blanket is installed. For older aircraft that are being retrofit for improved fire blocking performance, this permits re-use of the existing insulation blanket. The existing insulation blanket is removed from the frame members and the fire blocking material which has been cut to size is installed and attached to the frame members. The insulation blanket is then replaced on the inboard side of the fire blocking material and secured in place. Preferably, the fire-blocking material is treated with a water repellent substance to prevent absorption of moisture.
In an alternative embodiment of the invention, the lofted and/or foam insulation, and the fire-blocking layer are not encased within a protective covering. The fire-blocking layer is adhered to the insulation and extends past the edges of the insulation so that the fire-blocking layer may be attached to the aircraft frame members along both long edges of the insulation blanket. Preferably, the fire-blocking layer and attached lofted insulation are treated with a water repellent substance to prevent absorption of moisture.
In this application:
xe2x80x9cLofted insulationxe2x80x9d refers to thermal and/or acoustic insulation material with an aggregate density of no greater than one pound per cubic foot of material, which is readily compressible and which will substantially resume its original shape after removal of a compressive force.
A xe2x80x9cfire-blocking materialxe2x80x9d is a sheet material with an aggregate weight per unit area of one-quarter (0.25) pounds per square foot or less that exhibits a burn through time of 60 seconds or more when tested using the fire blocking material screening test described below in Example 2.
A xe2x80x9cfire-blocking insulation blanketxe2x80x9d is an insulation blanket that incorporates one or more layers of fire-blocking material or lofted and fire blocking insulation.
A xe2x80x9clofted and fire blocking insulationxe2x80x9d is lofted insulation with essentially uniform aggregate density that exhibits a burn through time of 60 seconds or more when specimens no greater than three inches thick are tested using the fire blocking material screening test described below in Example 2.
An xe2x80x9cinsulation blanketxe2x80x9d or xe2x80x9cblanketxe2x80x9d is an assembly of thermal and/or acoustic insulation and other materials which is formed to a specific shape and configuration for use in a specific structure such as an airplane, house, office building, warehouse, truck, bus, train, or ship.
A fire-blocking insulation blanket constructed and installed according to the present invention will remain secured in place for at least two minutes, and preferably for more than five minutes, when subjected to the full-scale test described in the report titled xe2x80x9cFull-Scale Evaluation of Aircraft Fuel Fire Bumthrough Resistance Improvements,xe2x80x9d published by the United States Department of Transportation, Federal Aviation Administration (FAA), Fire Safety Section in January, 1999. In the same test, no gap permitting flame penetration will form between the aircraft frame members and the edges of a blanket constructed and installed according to the present invention for at least two minutes, and preferably for more than five minutes. Because the FAA test is designed to simulate realistic conditions during a post-crash fuel fire, it is anticipated that blankets according to the present invention will provide superior protection from flame penetration under real-world conditions.
Another advantage offered by the present invention is reducing the cost of retro fitting existing aircraft with insulation blankets having improved fire-blocking properties. According to FAA regulations, every modification to an existing aircraft must be documented. In the case of insulation blankets, any modification that requires changes to design drawings will typically have to be incorporated into over a thousand drawings for every airplane model. Therefore, providing an improved insulation blanket that may be fabricated without requiring changes to the original blanket drawings can result in significant cost savings. The present invention may be practiced by placing a layer of fire blocking material adjacent to the outboard side of the insulation blanket. The fire blocking layer may be incorporated into one of the two pieces of polymer protective covering films typically used to encase the lofted insulation, or it may be separate from the protective covering. The fire blocking layer will typically have the same or similar geometry as the outboard piece of protective covering film. Therefore it may be cut from the same template as the original piece of protective covering. To document the change, the aircraft operator need only revise the bill of materials and part number for the insulation blankets to specify the replacement film incorporating a fire-blocking material. Therefore, the more time-consuming changes to the geometric blanket patterns, including drawings and templates, may be avoided.
Blankets constructed and installed according to the present invention are especially useful for providing economical and effective fire-blocking insulation for aircraft. However, such blankets may also be used to provide fire-blocking insulation to any structure, such as a ship, bus, or building, that utilizes frame members that are (a) sufficiently fire-resistant to hold a fire-blocking blanket in place for the desired period of time, (b) adjacent to the exterior of the space which is to be protected from fire, and (c) configured to permit installation of insulation blankets between and attached to adjacent frame members. It is anticipated that blankets according to the present invention will be advantageous whenever fire-blocking replacements for regular (non-fire-blocking) insulation blankets are needed. In addition, blankets according to the present invention will be especially advantageous as replacement blankets whenever there is a need to conserve use of relatively costly and/or heavy fire-blocking material, because efficient use is made of a minimum amount of fire-blocking material.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.